1. Field of the Invention
The present invention relates to novel pigment pastes, to cationic electrodeposition paints containing the novel pigment pastes and to the use of these paints in the process of cationic electrodeposition.
2. Brief Description of the Prior Art
In the formulation of paints and especially electrodeposition paints, an important factor is the introduction of pigments into the paint. The pigments are typically ground in a pigment grinding vehicle which acts as a dispersing agent to form a paste and the resultant pigment paste is blended with a main resinous vehicle and optionally diluents to form the paint. For electrodeposition paints, the pigment grinding vehicle preferably is a resinous material having the same charge as the main resinous vehicle so that it will electrodeposit with the main resinous vehicle. Typical pigment grinding vehicles for cationic electrodeposition are quaternary ammonium slat group-containing resins such as are described in U.S. Pat. Nos. 4,007,154 and 4,186,124. Also, ternary sulfonium salt group-containing resins such as described in U.S. Pat. 4,715,898 can also be used as pigment grinding vehicles.
One disadvantage associated with quaternary ammonium salt group-containing resins as pigment grinding vehicles is that they often result in relatively rough films. On the other hand, the sulfonium salt group-containing resins such as described in the aforementioned U.S. 4,715,898 offer an advantage over the quaternary ammonium salt group-containing resins in that they result in smoother electrodeposited films, particularly films which deposit at higher film builds. Unfortunately, it has been found that the sulfonium salt group-containing resins have a stability problem with lead-containing paints. Such paints for reasons which are not entirely understood are not particularly stable to the shearing forces the paint encounters when it passes through a recirculating pump typically used with industrial cationic electrodeposition baths. In addition, it has been found that lead-containing paints which additionally contain the pigment carbon black result in a particularly troublesome sedimentation which forms upon storage of the paint. Although the sedimentation problem can be overcome by using quaternary ammonium group-containing resins as the pigment grinding vehicles, rough films often result.